Precision temperature probe having fast response

ABSTRACT

A temperature probe ( 10 ) including a cylindrical thermally conductive housing ( 10 ) and a temperature sensor ( 18 ) employing a resistive temperature element ( 22 ) mounted therein. The temperature sensor ( 18 ) is mounted at one end of the housing ( 12 ) by a thermally conductive potting material ( 50 ). Signal wires ( 36 ) electrically couple to the resistive element ( 22 ) extend through an elongated insulated member ( 30 ) and out of an end of the housing ( 12 ) opposite the sensor ( 18 ). Changes in the temperature of the housing are quickly transferred to the resistive temperature element ( 22 ) through the conductive potting material ( 50 ). In one embodiment, the probe ( 10 ) is combined with a pressure transducer ( 60 ) to provide a pressure and temperature sensing device.

GOVERNMENT RIGHTS

[0001] This invention was made with Government support under contractnumber F29601-97-C-0001 awarded by the United States Air Force. TheGovernment has certain rights in this invention.

BACKGROUND OF THE INVENTION

[0002]1. Field of the invention

[0003] This invention relates generally to a temperature probe and, moreparticularly, to a temperature probe employing a resistive temperatureelement mounted within a protective housing by a thermally conductivematerial to provide a fast thermal response time.

[0004] 2. Discussion of the Related Art

[0005] Temperature probes are used in many applications for sensing thetemperature of a solid, liquid or gas. For example, temperature probesare used in certain laser systems to detect the temperature of hydrogenperoxide (BHP) used in the generation of the laser beam. Otherapplications include medical, pharmaceutical, food, chemical, aerospaceand industrial applications. In certain applications, it is important tomeasure the temperature accurately and very quickly.

[0006] Different classes of temperature sensors are known in the art tomeasure temperature. One class of temperature sensors employs resistiveelements, well known to those skilled in the art. As the temperature ofthe element increases or decreases, the resistance of the element alsoincreases or decreases providing an indication of the temperaturechange. A voltage signal applied to the element is measured to give areading of the resistance, and thus the temperature.

[0007] Known temperature probes that employ resistive elements typicallyhave a response time of seven seconds or more. Particularly, when thetemperature of the environment that the sensor is sensing changes, thesensor does not give the exact temperature reading for the change untilmore than seven seconds later. The probe response time is defined hereinas the time it takes the temperature sensor to respond through 63.2% ofthe total temperature change. This slow of a response time isunacceptable in many applications. The slow response time can beattributed to the fact that the resistive element is mounted within aprotective housing and air forms between the element and the housing.

SUMMARY OF THE INVENTION

[0008] In accordance with the teaching of the present invention, atemperature sensor employing a resistive temperature element isdisclosed that has a faster response time than those sensors known inthe art. The sensor includes an outer protective housing in which theresistive element is mounted. In one embodiment, the housing is acylindrical tube made of a thermally conductive material. The element ismounted at one end of the housing, and signal wires extend through thehousing and out of an opposite end of the housing. The element ismounted to an inside surface of the housing by a thermally conductivepotting material. Therefore, changes in temperature received by thehousing are quickly transferred to the element through the pottingmaterial giving a quick temperature response time.

[0009] Additional objects, advantages and features of the presentinvention will become apparent from the following description andappended claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a perspective view of a temperature sensor probe,according to an embodiment of the present invention;

[0011]FIG. 2 is a bottom view of the probe shown in FIG. 1;

[0012]FIG. 3 is a length-wise, cross-sectional view of the probe shownin FIG. 1;

[0013]FIG. 4 is a perspective view of the resistive element sensormounted within the probe shown in FIG. 1;

[0014]FIG. 5 is a length-wise, cross-sectional view of atemperature/pressure sensor assembly employing the temperature probeshown in FIG. 3; and

[0015]FIG. 6 is an end view of the assembly shown in FIG. 5.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The following discussion of the embodiments of the inventiondirected to a temperature sensor probe employing a resistive element ismerely exemplary in nature, and is in no way intended to limit theinvention or its applications or uses.

[0017]FIG. 1 is perspective view, FIG. 2 is a bottom view and FIG. 3 isa length-wise, cross-sectional view of a temperature sensor probe 10,according to an embodiment of the invention. The probe 10 includes anouter housing 12 defining a bore 14 therein that acts as a protectiveshield, and is made of a thermally conductive material, such as inconel,stainless steel, chromium, aluminum, etc. The housing 12 is cylindricalin this example because that shape lends itself to a more desirableconfiguration for many applications. Of course, in other examples, theshape of the housing 12 can be different to be more conducive for thatapplication. Further, the diameter, wall thickness and length of thehousing 12 is application specific. In one embodiment, the housing 12has an outer diameter of ⅛ of an inch, an internal diameter of 0.095inches and a length of 6 inches.

[0018] The housing 12 has an end cap 16 welded to and closing off oneend of the housing 12. In one embodiment, the end cap 16 has a thicknessof 0.01 inches. A thin film sensor 18 is mounted within the housing 12proximate the end cap 16, as shown. FIG. 4 is a perspective view of thesensor 18 separated from the probe 10. The sensor 18 is a thin filmsensor including a ceramic substrate 20 on which a resistive element 22is mounted, and is a commercially available device. A pair of connectingleads 24 are electrically coupled to the element 22, and extendtherefrom. In one embodiment, by way of non-limiting example, the sensor18 has a thickness of 1.3 mm, a width of 2.0 mm and a length of 2.3 mm.The resistive element 22 is 100 Ω platinum in this embodiment, but canbe other conductive materials. The connecting leads 24 are 30 AWG and 15mm in length, and are made of 95% Au and 5% Pd.

[0019] A cylindrical insulating member 30 is positioned within thehousing 12 proximate the sensor 18, and extends the length of thehousing 12, as shown. One end of the member 20 is secured to the sensor18 by a suitable sealing bond 32, and the opposite end of the member 20is secured to an inside surface of the housing 12 by a cylindricalsealing bond 34. Signal wires 36 are electrically coupled to the leads24 and extend through parallel bores 38 in the member 30 and out of anend 40 of the probe 10 opposite the end cap 16. The wires 36 areelectrically coupled to an electrical receptacle 44 mounted to the end40. The receptacle 44 includes terminals 46 electrically coupled to thewires 36 to provide the signal to the sensor 18.

[0020] According to the invention, the sensor 18 is mounted to theinside of the housing 12 by a potting material 50. The potting material50 is a thermally conductive material that provides a good thermalcontact between the sensor 18 and the housing 12. Therefore, when theoutside of the housing 12 receives a temperature change, that change intemperature is immediately transferred to the sensor 18 through thepotting material 50.

[0021] The potting material 50 can be any thermally conductive materialsuitable for the purposes described herein. In one embodiment, thematerial 50 is a mixture of silver particles suspended in a resin andsuitable solvent. The potting material 50 is inserted into the housing12 as a liquid so that when the sensor 18 is inserted into the housing12 it causes the liquid potting material to fill in the spaces betweenthe sensor 18 and the end cap 16, and the sensor 18 and the inside wallof the housing 12, as shown. In one embodiment, the sensor 18 isinserted into the housing 12 so that a 0.5 mm gap, filled with thepotting material 50, is provided between the sensor 18 and the end cap16. Once the sensor 18 is positioned within the liquid potting material50 in the housing 12, the housing 12 is cured to harden the pottingmaterial 50.

[0022] The temperature probe 10 was measured for response time by asuitable signal condition module, such as the SCM 5B35-1438, coupled toa memory oscilloscope, such as the Tektronic Model 7H-730A. Temperatureresponse times 15 to 20 times faster than those known in the art weremeasured. In one test, the probe 10 was immersed in an ice bath, andmeasured a 540 msec response time when the bath was still, and a 320msec when the bath was agitated.

[0023] The probe 10 described above can be made by any suitable assemblyprocess. In one embodiment, a specific procedure is followed tofabricate the probe 10, according to the invention. The following stepsdescribe that process in general detail as a non-limiting example. Thecylindrical housing 12 is cut and deburred. The end cap 16 is fabricatedand welded to one end of the cut housing 12. The housing 12 and the endcap 16 are then degreased and ultrasonically cleaned. Next, the housing12 and end cap 16 are oven dried and sealed in a protective bag. Thesignal wires 36 are then soldered to the leads 24. The wires 36 areinserted into the channels 38, and the sensor 18 is bonded to the member20 with the seal bond 32, such as an M-bond GA-61. The sensor and memberassembly is then oven cured per the M-bond GA-61 specification. Themember and sensor assembly is then held in a vice, and a predeterminedamount of the liquid potting material 50 is placed on top and around thesensor 18.

[0024] The housing 12 is also held in a vice, and the liquid pottingmaterial 50 is inserted into the housing 12 using a syringe. The housing12 is then installed on a vibration table and the vibration table isoperated at approximately 100 Hz, and approximately 1-2 milspeak-to-peak displacement. The member and sensor assembly is insertedvertically into the vibrating housing 12 to a predetermined depth markedon the member 20. The inserted member and sensor assembly is centered inthe housing 12 using three steel wedges firmly placed at 120 degrees.The complete assembly is cured from ambient to 200° C. over 180 minutes,and then cooled at ambient. The temperature and time of the curingprocess is selected so that the solvent in the potting materialgradually evaporates without the formation and permanent inclusion ofminiature air bubbles that would severely affect the thermal performanceof the probe 10.

[0025] The probe 10 described above can be used in combination withother types of sensing devices. For example, a temperature/pressuresensor assembly 58 is shown in a length-wise, cross-sectional view inFIG. 5 and an end view in FIG. 6, and is a combination of the probe 10and a pressure transducer 60, according to the invention. In oneembodiment, the pressure transducer 60 embodies the series PT700transducer, available from Stellar Technologies, Inc. The probe 10 isinserted into an enclosure 62 through a bore 64 extending through an endpiece 66 attached to one end of the enclosure 62, so that the end cap 16of the probe 10 extends therefrom, as shown. The end piece 66 includes athreaded connector 68 that allows the transducer 60 to be threadablyconnected to a suitable opening, as would be well understood to thoseskilled in the art. The bore 64 defines a pressure port of thetransducer 60. The probe 10 is secured to a base plate 72 mounted withinthe enclosure 62, as shown. The probe 10 is held within the bore 64 byextended support fins 70 placed at three locations separated by 120°around an outside of the housing 12, as shown.

[0026] A sensing tube 74 is mounted within the enclosure 62, where afirst end flange 76 of the tube 74 is mounted to the end piece 66 and asecond end flange 78 of the tube 74 is mounted to the base plate 72, asshown. A chamber 80 within the sensing tube 74 is coaxial with the bore64. A metal film, full bridge rectifier, strain gage pressure sensor 84is mounted to an outside surface of the sensing tube 74 within theenclosure 62. An electrical receptacle 98 including pin terminals 96 ismounted and hermetically sealed to an end of the enclosure 62 oppositethe end piece 66. A signal conditioning module 88 is mounted within theenclosure between the base plate 72 and the receptacle 98. Four signallines, one for each rectifier in the sensor 84, is electrically coupledto the sensor 84 and the conditioning module 88. Likewise, the signallines 36 are coupled to the conditioning module 88.

[0027] An external pressure change is transferred to the chamber 80through the bore 64, and causes the tube 74 to expand or contract inresponse thereto. This expansion or contraction of the tube 74 changesthe strain on the pressure sensor 84, giving an electrical indicationthereof to its full bridge rectifier. The signal lines 86 areelectrically coupled to each leg of the bridge rectifier in the sensor84 to give a measure of the strain on the sensor 84, in a manner that iswell understood in the art. The conditioning module 88 processes thesignals on the signal wires 86 and 36 and provides selective pressuresensing and temperature sensing outputs on signal wires 90. The signalwires 90 are coupled to the connector pins 96 of the electricalreceptacle 98 sealed to the enclosure 62. The receptacle 98 iselectrically coupled to any suitable measuring circuit (not shown) toprovide a display of the temperature and pressure, as would be wellunderstood to those skilled in the art.

[0028] Various parameters and specifications can be used for thecombination of the temperature probe 10 and the pressure transducer 60assembly discussed above. In one embodiment, the pressure transducer 60has a response time of 10 msec at 90% FS, a maximum 10 microampspeak-to-peak output and a pressure range of 0-350 psia FS. Thetemperature probe 10 has a response time of 10 msec at 90% FS, atemperature coefficient of 0.00385, a maximum element excitation of 1.0mA, a temperature range of −23° C.-27° C. FS and an output ripple of amaximum 10 microamps peak-to-peak.

[0029] The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

What is claimed is:
 1. A temperature probe comprising: a housing made ofa thermally conductive material, said housing including an innerchannel; a temperature sensor mounted within the channel, said sensorincluding a resistive element responsive to temperature changes andsignal wires connected thereto; and a thermally conductive pottingmaterial holding the sensor within the housing, said potting materialbeing in contact with the resistive element and the housing so as totransfer temperature changes from an outer surface of the housing to theresistive element.
 2. The probe according to claim 1 wherein the pottingmaterial is made of a solvent including interspersed silver particles.3. The probe according to claim 1 wherein the potting material is acured liquid solvent.
 4. The probe according to claim 1 wherein thehousing is a cylindrical tube, said sensor being positioned at one endof the housing therein.
 5. The probe according to claim 4 furthercomprising an elongated insulating member, said signal wires extendingthrough channels in the insulating member and out of an end of thehousing opposite the sensor.
 6. The probe according to claim 5 whereinthe insulating member is bonded to the sensor and to an inside wall ofthe housing.
 7. The probe according to claim 1 wherein the housingincludes a flat end cap, said sensor being mounted within the housingproximate the end cap.
 8. The probe according to claim 1 furthercomprising an electrical terminal mounted to the housing, said signalwires being electrically connected to the terminal.
 9. The probeaccording to claim 1 wherein the sensor is suspended within the pottingmaterial so that the distance between an internal surface of the channeland the sensor is about 0.5 mm.
 10. The probe according to claim 1further comprising a pressure transducer including an enclosure, saidprobe extending through a pressure port in the enclosure, said pressuretransducer including a pressure sensor mounted within the enclosure thatsenses a pressure change transferred through the pressure port.
 11. Theprobe according to claim 10 wherein the pressure transducer includes apressure sensing tube mounted within the enclosure, said probe extendingthrough the pressure sensing tube, said pressure sensor being mounted toan outer surface of the pressure sensing tube.
 12. The probe accordingto claim 10 wherein the pressure sensor is a metal film, full bridgerectifier strain gage.
 13. The probe according to claim 10 furthercomprising a signal conditioning module, wherein the signal wires fromthe temperature sensor and signal wires from the pressure sensor areelectrically coupled to the signal conditioning module, said signalconditioning module including a pair of output signal lines coupled toan electrical connector.
 14. A resistive element temperature probe forsensing a temperature of an environment, said probe comprising: acylindrical housing made of a thermally conductive material, saidhousing including an internal bore; a temperature sensor mounted withinthe bore at one end of the housing, said sensor including a resistiveelement responsive to temperature changes mounted on a ceramic substrateand a pair of signal wires connected thereto; a cylindrical insulatingmember mounted to the sensor and to an inside surface of the bore of thehousing, said signal wires extending through channels in the insulatingmember and out of an end of the housing opposite the sensor; and athermally conductive potting material formed in the bore within thehousing and securing the sensor within the housing, said pottingmaterial being in contact with the resistive element and the housing soas to transfer temperature changes from an outer surface to theresistive element, said potting material being a cured liquid solvent.15. The probe according to claim 14 wherein the potting materialincludes interspersed silver particles.
 16. The probe according to claim14 wherein the sensor is suspended within the potting material so thatthe distance between an internal surface of the channel and the sensoris about 0.5 mm.
 17. The probe according to claim 14 further comprisinga pressure transducer including an enclosure, said probe extendingthrough a pressure port in the enclosure, said pressure transducerincluding a pressure sensor mounted within the enclosure that senses apressure change transferred through the pressure port.
 18. The probeaccording to claim 17 wherein the pressure transducer includes apressure sensing tube mounted within the enclosure, said probe extendingthrough the pressure sensing tube, said pressure sensor being mounted toan outer surface of the pressure sensing tube.
 19. The probe accordingto claim 17 wherein the pressure sensor is a metal film, full bridgerectifier strain gage.
 20. The probe according to claim 17 furthercomprising a signal conditioning module, wherein the signal wires fromthe temperature sensor and signal wires from the pressure sensor areelectrically coupled to the signal conditioning module, said signalconditioning module including a pair of output signal lines coupled toan electrical connector.
 21. A temperature/pressure sensor assembly formeasuring the temperature and pressure of an environment, said assemblycomprising: a pressure transducer housing including an end piece mountedto one end of the housing and an electrical receptacle mounted to anopposite end of the housing, and defining an enclosure chambertherebetween, said end piece including a pressure port extendingtherethrough; a pressure sensing tube mounted to the end piece andincluding a pressure sensing tube chamber therein, said pressure chamberand said pressure port being in fluid communication; a pressure sensormounted to an outside surface of the pressure sensing tube within theenclosure chamber; a temperature probe housing made of a thermallyconductive material, said temperature probe housing including aninternal channel, a first end and a second end, said first end of saidtemperature sensing housing extending through the pressure port and thepressure tube chamber; and a temperature sensor mounted within thechannel proximate the second end of the temperature probe housing, saidsensor including a resistive element responsive to temperature changesin the environment.
 22. The assembly according to claim 21 furthercomprising a thermally conductive potting material for holding thetemperature sensor within the temperature probe housing, said pottingmaterial being in contact with the resistive element and the temperatureprobe housing so as to transfer temperature changes from an outersurface of the temperature probe housing to the resistive element. 23.The assembly according to claim 22 wherein the potting material is madeof a solvent including interspersed silver particles.
 24. The assemblyaccording to claim 22 wherein the potting material is a cured liquidsolvent.
 25. The assembly according to claim 21 further comprising anelongated insulating member, said temperature sensor including signalwires extending through channels in the insulating member and out of thefirst end of the temperature probe housing.
 26. The assembly accordingto claim 25 wherein the insulating member is bonded to the temperaturesensor and to an inside wall of the temperature probe housing.
 27. Theassembly according to claim 21 wherein the temperature probe housingincludes a flat end cap mounted to the second end of the temperatureprobe housing, said temperature sensor being mounted within thetemperature probe housing proximate the end cap.
 28. The assemblyaccording to claim 21 wherein the pressure sensor is a metal film, fullbridge rectifier strain gage.
 29. The assembly according to claim 21further comprising a signal conditioning module, wherein temperaturesensor signal wires and pressure sensor signal wires are electricallycoupled to the signal conditioning module, said signal conditioningmodule including a pair of output signal lines coupled to the electricalreceptacle.
 30. A method of measuring the temperature and/or pressure ofan environment, comprising: bonding a resistive temperature elementwithin a channel of a thermally conductive housing with a thermallyconductive potting material; and placing the housing in contact with theenvironment so that temperature changes of the environment aretransferred through the potting material to the resistive element. 31.The method according to claim 30 wherein the potting material is made ofa solvent including interspersed silver particles.
 32. The methodaccording to claim 30 wherein the resistive temperature element ismounted within the channel by inserting the conductive potting materialin liquid form into the housing, positioning the resistive temperatureelement within the channel so that the liquid potting material formsaround the temperature element and is in contact with the housing, andcuring the liquid potting material.
 33. The method according to claim 30further comprising positioning the conductive housing within a pressureport of a pressure transducer so that the housing is secured therein andthat an end of the housing including the resistive temperature elementextends therefrom.